TV power consumption testing vs. specs: Ask the Editors

(Credit: CNET)

Q: I am very interested in a TV's power performance, and would like to double check something I found on the site. I saw that on the specs page for the Panasonic TH-50PZ800U plasma, you guys had that the power consumption is 692 watts. Whereas on your 104 HDTVs' power consumption compared chart, the same television is listed as using only 191.22 watts, and is said to be a "good performer." Can you help me out and let me know which one is the correct one or why they are 400 watts different? -- Joe, via email

A:The short answer is pretty simple, Joe: the 692-watt spec cited on CNET, according to that TV's user manual, corresponds to the maximum power consumption, whereas the 191-watt result of our testing reflects a real-world usage scenario. The long answer is a bit more complex, especially for Panasonic plasmas.

Plasmas, unlike LCDs and rear-projection microdisplays, use more power when the screen shows bright scenes and less when it shows dark scenes. So as you can imagine, maximum power consumption equates to the screen showing an extremely bright scene all the time. That's not what happens in the real world, which is one reason we use a standardized test clip (a half-hour of That '70s Show, if you're wondering) for our testing. The difference between an all-bright screen and that clip is one big factor in the difference between the two numbers.

More important, however, are the TV's picture settings: bright settings use more power. Many HDTVs this year include a question that asks, during initial setup, whether the TV is being used in the store or at home. On the Panasonic plasmas we've tested, if you answer "home" the TV sets the default picture mode to "Standard," whereas selecting "store" sets it to "Vivid." While we applaud the home/store option in general since it leads to better energy efficiency, Panasonic cheated a bit with its standard modes this year.

If you check out the Juice Box for that review, you'll see that Standard actually consumes significantly fewer watts than Calibrated (191 vs. 286). In other words, we found Standard way too dim for normal use, and had to turn up the Contrast control to get the picture into the realm we deemed bright enough. We think most users will want to do the same to get acceptable brightness.

Despite "cheating" by putting in an overly-dim Standard mode, Panasonic gets away with it because our test specifies that we report the "default" picture setting for the big chart. We're not the only ones. The Energy Star 3.0 program requirements for TVs (PDF), which incorporates the IEC 62087 specification for power consumption testing (PDF), says "For products shipped with a forced menu where the customer must select upon initial start up the mode in which the product will operate, section 11.4.8 states that testing must be conducted in 'standard mode.'" Putting in a dim Standard mode was, we believe, the only way the TV could qualify for the 3.0 spec. In case you're wondering, that version of the spec isn't supposed to be deployed until November 1, 2008, so the Energy Star sticker on the Panasonic and all other HDTVs manufactured before that date applies to an earlier version with far less-stringent qualifications.

One added note: before the end of 2008 CNET's power consumption test methodology will shift to using the official IEC 62807 method, so our numbers after that time should be comparable with manufacturer specs and other outlets' tests (like Crutchfield's). When we make the shift, we'll let you know right here.